Frank Watson Dyson was educated at Bradford Grammar School and Trinity College, Cambridge, where he was second wrangler in the mathematics tripos in 1889. He was elected a fellow of Trinity in 1891 and awarded an Isaac Newton studentship to undertake research in astronomy.

In 1894 he accepted the post of chief assistant at the Royal Observatory, Greenwich, under William Christie. Dyson’s task was measuring the positions of stars for the Observatory’s contribution to the ‘International Astrographic Catalogue’. In 1906 he took up the posts of Astronomer Royal for Scotland and Regius Professor of Astronomy at Edinburgh University.

When Christie retired in 1910, Dyson returned to Greenwich as the ninth Astronomer Royal. He became interested in solar eclipses, organizing a number of expeditions and developing eclipse spectroscopy. In 1917 he explained that the solar eclipse due in 1919 could be used to provide an observational test for Einstein’s general theory of relativity. The theory predicted that stars seen close to the eclipsed sun would appear to be shifted by a small but measurable distance. Dyson presented his observation findings at the Royal Astronomical Society late in 1919, showing that the collected data supported Einstein’s prediction.

Dyson’s work at the Royal Observatory also required an interest in the measurement of time. He introduced the Shortt free-pendulum clock for the time service in 1924. He was also approached by John Reith to see if the Observatory would provide the time signals for the BBC. Dyson determined the system of six pips, with the final denoting the hour. From 1927 onwards, the time signal was broadcast around the world, principally, at least initially, for the benefit of shipping.

He was knighted in 1915 and appointed KBE in 1926. He retired in 1933 and died at sea on board the ‘Ascanius’ returning from Australia on 25 May 1939. He was buried at sea the same day.

The artist, Ernest Moore, was born in Barnsley in 1865 and specialized in portraits.This portrait of Dyson was exhibited as part of 'Men of Yorkshire' at the Walker Gallery, New Bond Street, London, 4-18 November 1925. Moore died in 1940.